1. Field of the Invention
The present invention relates to a stator coil constructed by joined conductor segments for rotary electric machines and a method for manufacturing the same.
2. Description of the Related Art
There have been disclosed joined conductor segment stator coils, wherein a plurality of conductor segments inserted into slots of a stator core are sequentially connected one by one. For example, a method for manufacturing the joined conductor coil (joined conductor segment stator coil) by utilizing nearly U-shaped conductor segment in JP No. 3118837.
In JP No. 3118837, legs of a pair of the nearly U-shaped conductor segments are inserted into an entrance of, and are projected from opposite exits of, a pair of slots distant from each other by a magnet pole pitch of a rotor. Then, the projected legs are bent toward the circumferential direction of the rotor and are sequentially joined together.
Therefore, the conductor segment comprises: a nearly U-shaped (nearly V-shaped after bending process as explained below: cf. FIG. 13) head portion; a pair of slot conductor portions which are inserted (along the core axis from one end of a pair of slots and are staying in the pair of slots; and a pair of projected end portions projected from the other end of the pair of slots. Further, the tips of the projected end portions in the pair are joined with each other. Here, in the present specification, the projected end portion together with the slot conductor portion is sometimes denoted as a leg of segment. The head portion is a head side coil end, while the projected end portion is an end side coil end.
Further, there are disclosed also in JP3118837 co-axially disposed two rings for holding four legs of a pair of a small head segment and a large head segment surrounding the small head segment. The rings are relatively rotated in order to form a oblique end portion (a pair of legs oblique toward the circumferential direction of the rotor).
Further, there are disclosed in JP2000-139049A co-axially disposed four rings for receiving four legs of a pair of a small and large segment. Here, the large segment surrounding the small segment.
Further, there is disclosed in JP2001-45721A a method for manufacturing the above-mentioned segment pair (segment set).
An exemplary method for manufacturing the joined conductor coil as disclosed in the above-mentioned prior art documents is explained.
First, a required number of pine needle segments are prepared and are bent to have U-shaped heads. Then, a pair of legs of the segments are bent along the circumferential direction by a magneto pole pitch and required number of pairs of segments are arranged along the circumreferential direction in order to simultaneously insert them into all the slots of the core. The two rings (co-axially disposed) with a plurality of holes as shown in FIG. 3 in JP No. 3118837 may be employed. Concretely, the segment legs are inserted into the outer and inner rings at the same circumferential direction and then the inner and outer rings are relatively rotated in order to deform the head portion of the segment in such a manner that the head portion is made open like a V-shape. Further, a process step follows for inserting the V-shaped deformed segments which are arranged along the circumeferential direction into the slots of the stator core. Concretely, holding the head portions, the segment sets are pulled out from the rings and are inserted into the slots.
Further, a process step follows for bending, preferably by a half pitch of the magneto pole, the projected end portion along the circumferential direction. The two rings (co-axially disposed) with a plurality of holes as shown in FIGS. 4 and 5 in JP No. 3196738 may be employed for the above-mentioned bending step. The projected end portion is inserted into the holes, then the inner and outer rings are relatively rotated by a half pitch of the magnet pole and then the projected end portion is bent by the half pitch along the circumferential direction. The radius of curvature at the bending point can preferably be made larger, if the rings are pressed along the axial direction toward the projectted end portion. Further, a process step follows for welding the projected end portions each other in a prescribed order.
Thus, a phase coil is endlessly formed. Therefore, terminals for each phase are formed by cutting the head portion of the U-shaped segment. If the terminal is made long beforehand, the long terminal can be utilized for a crossover for a neutral point. It is noticed that the terminal is provided at the head portion side, because the long terminal wire is obstructive against the welding of the projected end portions.
The joined segment stator coil as manufactured by the above-explained processes has been employed for a stator coil of AC dynamo for automotive vehicles.
However, the conventional joined segment stator coil has a disadvantage that the width of the head portion becomes greater than that of the pair of legs, because the head portion with a prescribed radius of curvature is bent by an electric angle π/2. The radius of curvature is preferably as small as possible. However, the radius reduction is limited, because a damage of insulating coating on the smaller head portion should be prevented and the segment should be easily bent.
Accordingly, the width of the head portion of the large segment inevitably becomes greater than that of its legs. This is because four legs of the small and large segments must be received in the four portions along the radial direction of the slots.
Further, when the linear portions held in the rings are bent along the circumferential direction before insertion into the stator core, the small segment sink more deeply toward the rings than the large segment. Thus, it became clear that the smaller head portion is apt to contact with the larger head portion near the linear portion of the large segment, thereby degrading an insulation between them.
FIG. 14 is a side view of a segment set of a small segment 332 and large segment 331 before bending, while FIG. 15 is a side view of the segment set after bending. As shown in FIGS. 14 and 15, the large segment 331 comprises a larger head portion 3a and a pair of linear leg portions 3b, while the small segment 332 comprises a smaller head portion 3a′ and a pair of linear leg portions 3b′.